Ammonium polyphosphate is a typical halogen-free phosphor-and-nitrogen type flame retardant, which has the advantages of low toxicity, environmentally friendly, high efficiency and low cost, thus it has been widely used in the flame retardant. However, with ammonium polyphosphate is accepted and widely used, its own problems have become increasingly prominent, such as, hydroplaning, poor water resistance, the ordinary compatibility of the resin, which causes the physical properties of the resin severely deteriorated after the modification of traditional ammonium polyphosphate. If it is applied in larger products, the products will produce gas marks. If it is used in the electrical components which contacts with water vapor for a long period of time, there will be a problem of precipitation and the like. To a certain extent, it can't replace the bromine-antimony flame retardant completely, which limits the application of ammonium polyphosphate flame retardant.
In recent years, many scholars have focused that the ammonium polyphosphate is not resistant to hydrolysis and have done a lot of work. At present, the research on coating treatment of ammonium polyphosphate is mainly classified into seven categories: the first one is microencapsulation treatment of ammonium polyphosphate with melamine formaldehyde resin as disclosed in CN103980541A, CN103483873A and etc.; the second one is microencapsulation treatment of ammonium polyphosphate with epoxy resin as disclosed in CN101362836 and etc.; the third one is surface treatment of ammonium polyphosphate with silicone oil as disclosed in CN104479172A and etc.; the fourth one is grafting treatment of ammonium polyphosphate with organic amine as disclosed in CN103382267A, CN103694742A and etc.; the fifth one is firstly microencapsulation treatment with melamine formaldehyde resin, then double coated treatment with acrylate as disclosed in CN103554999A, CN103588992A and etc.; the sixth one is microencapsulation treatment of ammonium polyphosphate with urea resin as disclosed in CN104513407A and etc.; the seventh one is introducing the silane structure during the synthesis of ammonium polyphosphate as disclosed in CN104098789A and etc. . . . .
The first one to the sixth one above are coating or grafting treatment of ammonium polyphosphate itself, wherein the coating of microencapsulation described in the first, the second, the fifth and the sixth one is helpful to reduce viscosity and water solubility, but at the same time, the initial decomposition temperature of the modified ammonium polyphosphate products is reduced. There are risks of early decomposition, color change, and not able to be resistant to high temperature processing in the process of high temperature application for long time. The surface wall capsule can be damaged under certain processing or treatment conditions, causing the body of ammonium polyphosphate is partially exposed. There is still a problem of poor water resistance; meanwhile in the process of high temperature processing, ammonium polyphosphate coated with melamine formaldehyde resin may have the risk of releasing formaldehyde, which has bad effect on the property of materials and environment. The third one is coating with silicone oil, which can improve the viscosity, water solubility and dispersibility of ammonium polyphosphate surface, but the coating can be incomplete, meanwhile during thermal processing and shearing process, the silicone oil coating will be damaged, causing poor water resistance later. The fourth one is grafting with organic amine. The reaction activity of high polymerized ammonium polyphosphate has been weak, and it has difficulty in grafting with organic amine. The grafting will be incomplete, and the final modified ammonium polyphosphate can't achieve the expected high temperature and humidity resistance effect. The seven one is introducing silane group during the synthesis of ammonium polyphosphate. The process is more complicated and takes longer time, meanwhile it can't ensure there is no acid polyphosphate and small molecule in later products, and can also affect the water solubility, the high temperature and humidity resistance effect.